Best open-source alternatives to Microsoft 365

Nextcloud Server is a self-hosted collaboration and file platform for individuals, teams, and organizations that want control over their data. It provides a central place to store files and also supports contacts, calendars, communication features, and sharing across devices. The project is designed for users who want cloud-like functionality on infrastructure they control, whether at home or in a company environment. It is extensible through a large app ecosystem, includes security features such as encryption and two-factor authentication, and can be deployed by self-installation, through hosting providers, or via appliances and preinstalled devices.

Overleaf is a self-hostable, open-source online editor for LaTeX documents. It is designed for collaborative writing, letting multiple users work on projects in real time through a web interface. The README also notes that a hosted version is available at overleaf.com, while the community edition can be run locally and modified by contributors. The project is aimed at teams, labs, and organizations that need browser-based LaTeX editing, with an enterprise offering for environments that require additional security and administration capabilities. The community edition is presented as suitable only for trusted-user environments because it lacks sandboxed compiles, while the server pro offering adds features such as SSO via LDAP or SAML, administration, and collaboration enhancements like tracked changes.

Mail-in-a-Box is a self-hosted email appliance designed to make running a personal mail server simple. It turns a fresh Ubuntu 22.04 LTS 64-bit machine into a configured stack for receiving, sending, and managing email, with a focus on privacy, decentralization, and low-effort deployment. The project bundles the major mail-server components needed for a complete setup, including SMTP, IMAP, webmail, spam filtering, DNS, TLS certificates, backups, and monitoring. It also provides a control panel for managing users, aliases, DNS records, and backups, plus an API for control-panel actions. The README positions it for individuals who want to self-host email without dealing with a highly customizable or manually assembled server environment.

Stalwart is an open-source mail and collaboration server aimed at organizations that need a secure, scalable platform for email and groupware. It combines traditional mail protocols with collaboration features, making it suitable for teams that want a self-hosted alternative for messaging, calendaring, contacts, and file sharing. The project supports a broad set of protocols including IMAP, JMAP, POP3, SMTP, CalDAV, CardDAV, and WebDAV. It also emphasizes operational features such as multi-tenancy, authentication and authorization controls, filtering for spam and phishing, observability, high availability, and web-based administration. The README presents it as a Rust-based server designed for reliability and growth from small deployments to large clusters.

CryptPad is a self-hostable collaboration suite focused on privacy and end-to-end encryption. It lets people work together on shared content in real time while keeping the stored data encrypted, so the service operators cannot read the content if the server is compromised. The project is open source and is intended for users and organizations that want collaborative editing without giving the hosting provider access to the underlying documents. The platform includes several collaborative applications such as documents, spreadsheets, presentations, forms, kanban boards, code, rich text, and whiteboards. It supports deployment for development and production, with Docker-based setup available and separate installation guidance for administrators. The README also points users to documentation, release notes, translation infrastructure, community forums, and security guidance for using instances safely.

Sandstorm is a self-hostable web productivity suite designed for people who want to run their own server and install web apps as easily as mobile apps. It positions itself as a security-hardened web app package manager rather than a single application, enabling users to deploy apps for common productivity tasks such as documents, spreadsheets, blogs, git repositories, and task lists. The project is open source and targets x86-64 Linux systems. Its README points users to documentation for installation, usage, security practices, and developer packaging, suggesting it serves both administrators setting up a Sandstorm instance and developers publishing apps for the ecosystem. A public demo and documentation site are also provided.

ONLYOFFICE Docs is a self-hosted online office suite intended for teams and organizations that need collaborative document editing inside their own infrastructure or within third-party platforms. It provides editors for text documents, spreadsheets, presentations, forms, PDFs, and diagrams, with compatibility for Office Open XML formats. The project is designed to integrate with products such as ONLYOFFICE DocSpace, ONLYOFFICE Workspace, and external sync-and-share systems like Nextcloud, Moodle, ownCloud, Seafile, and Odoo. It emphasizes real-time co-editing, review and change tracking, version history, plugins, and a range of editor features such as spell-checking, accessibility options, and dark mode. The README also describes multiple editions, including a free community edition and paid enterprise/developer offerings.

Modoboa is a mail hosting and management platform designed to help administrators run and manage email services through a modern web interface. It combines administration tools with user-facing features such as webmail, calendar, address book, filters, and autoreply handling, making it suitable for organizations that need both mailbox management and day-to-day mail access. The project integrates with common mail infrastructure like Postfix and Dovecot and uses a SQL database as the central coordination point among components. It is built in Python 3 with Django and Vue, and its functionality is organized as extensions to keep the platform modular and easy to extend. The README also points users to an official installer, documentation, and a demo installation for evaluation.

NextcloudPi is a community project that packages Nextcloud into a ready-to-use appliance-style distribution. It targets users who want a preconfigured Nextcloud deployment on Raspberry Pi, Odroid, Rock64, virtual machines, LXD/LXC containers, or a Debian-based host without assembling the stack manually. The project bundles the application with supporting services and administration tools, including a web panel and a command-line configuration utility. It also provides a wide set of convenience and hardening extras such as HTTPS redirection, backups and restores, firewalling, fail2ban, dynamic DNS, automatic updates, and storage features like BTRFS snapshots and USB automounting.

SOGo is presented as a collaborative free and open source groupware project. The README focuses on how contributors can help improve the software through documentation, translations, feature ideas, discussion, and code patches, rather than describing end-user workflows in detail. It also explains how to obtain the source code for SOGo and its related components, including SOPE and the Thunderbird connector extension, and points readers to compilation instructions in the project FAQ. The document further highlights the software’s internationalization support by listing a broad set of official translations and maintainers, suggesting a mature, community-driven project with a strong emphasis on multilingual use and contribution.